In the production of hydrocarbons from hydrocarbon-bearing unconsolidated formations, a well is provided which extends from the surface of the earth into the unconsolidated or poorly consolidated formation. The well may be completed by employing conventional completion practices, such as running and cementing casing in the well and forming perforations through the casing and cement sheath surrounding the casing, thereby forming an open production interval which communicates with the formation.
Hydrocarbon production from subterranean formations commonly includes a wellbore completed in either cased hole or open-hole condition. In cased-hole applications, a wellbore casing is placed in the wellbore and the annulus between the casing and the wellbore is filled with cement. Perforations are typically made through the casing and the cement into the production interval to allow formation fluids (such as, hydrocarbons) to flow from the production interval zones into the casing. A production string is then placed inside the casing, creating an annulus between the casing and the production string. Formation fluids flow into the annulus and then into the production string to the surface through tubing associated with the production string. In open-hole applications, the production string is directly placed inside the wellbore without casing or cement. Formation fluids flow into the annulus between the formation and the production string and then into production string to surface.
The production of hydrocarbons from unconsolidated or poorly consolidated formations may result in the production of sand along with the hydrocarbons. Produced sand is undesirable for many reasons. It is abrasive to components within the well, such as tubing, pumps and valves, and must be removed from the produced fluids at the surface. Further, it may partially or completely clog the well, thereby requiring an expensive workover. In addition, the sand flowing from the formation may leave a cavity, which may result in the formation caving and collapsing of the casing.
A technique commonly employed for controlling the flow of sand from an unconsolidated or poorly consolidated formation into a well involves the forming of a gravel pack in the well adjacent part or all of the unconsolidated or poorly consolidated formation exposed to the well. Thereafter, hydrocarbons are produced from the formation through the gravel pack and into the well. Gravel packs have generally been successful in mitigating the flow of sand from the formation into the well.
Several downhole solid, particularly sand, control methods being practiced in industry are shown in FIGS. 1(a), 1(b), 1(c) and 1(d). In FIG. 1(a), the production string or pipe (not shown) typically includes a permeable outer member (such as, a sand-screen or sand control device) 1 around its outer periphery, which is placed adjacent to each production interval. The sand-screen prevents the flow of sand from the production interval 2 into the production string (not shown) inside the sand-screen 1. Slotted or perforated liners can also be utilized as sand-screens or sand control devices. FIG. 1(a) is an example of a screen-only completion with no gravel pack present.
As discussed above, one of the most commonly used techniques for controlling sand production is gravel packing wherein sand or other particulate matter is deposited around the production string or well-screen to create a downhole filter. FIGS. 1(b) and 1(c) are examples of cased-hole and open-hole gravel packs, respectively. FIG. 1(b) illustrates the gravel pack 3 outside the screen 1, the wellbore casing 5 surrounding the gravel pack 3, and cement 8 around the wellbore casing 5. Typically, perforations 7 are shot through the wellbore casing 5 and cement 8 into the production interval 2 of the subterranean formations around the wellbore. FIG. 1(c) illustrates an open-hole gravel pack wherein the wellbore has no casing and the gravel pack material 3 is deposited around the wellbore sand-screen 1.
A variation of a gravel pack involves pumping the gravel slurry at pressures high enough so as to exceed the formation fracture pressure (“Frac-Pack”). FIG. 1(d) is an example of a Frac-Pack. The well-screen 1 is surrounded by a gravel pack 3, which is contained by a wellbore casing 5 and cement 8. Perforations 6 in the wellbore casing allow gravel to be distributed outside the wellbore to the desired interval. The number and placement of perforations are chosen to facilitate effective distribution of the gravel packing outside the wellbore casing to the interval that is being treated with the gravel-slurry.
One problem associated with gravel packing, especially with gravel packing long or inclined intervals, arises from the difficulty in completing packing the annulus between the screen and the casing for in-casing gravel packs or between the screen and the side of the hole for open hole or under-reamed gravel packs. Incomplete packing is often associated with the formation of sand “bridges” in the interval to be packed which prevent placement of sufficient sand below that bridge, for top down gravel packing, or above that bridge, for bottom up gravel packing. The problem associated with bridge formation is often circumvented by using alternate path technology, which provides separate pathways for sand laden slurry to reach locations above or below the sand bridge or bridges.
If the sand screen is damaged or impaired, sand infiltration may result causing flow impairment. Flow impairment during production from subterranean formations can result in a reduction in well productivity or complete cessation of well production. This loss of functionality may occur for a number of reasons, including but not limited to, migration of fines, shales, or formation sands, inflow or coning of unwanted fluids (such as, water or gas, formation of inorganic or organic scales, creation of emulsions or sludges), accumulation of drilling debris (such as, mud additives and filter cake), mechanical damage in sand control screen, incomplete gravel pack, and mechanical failure due to borehole collapse, reservoir compaction/subsidence, or other geomechanical movements.
Current industry well designs include little, if any, redundancy in the event of problems or failures resulting in flow impairment from well-screen failure. In many instances, the ability of a well to produce at or near its design capacity is sustained by only a “single” barrier to the impairment mechanism (for example, screen for ensuring sand control in unconsolidated formations). In many instances the utility of the well may be compromised by impairment occurring in a single barrier. Therefore, overall system reliability is very low. Flow impairment in wells frequently leads to expensive replacement drilling or workover operations.
The current industry standard practice utilizes some type of sand screen either alone or in conjunction with artificially placed gravel packs (sand or proppant) to retain formation sand. All of the prior art completion types are “single barrier” completions, with the sand screen being the last “line of defense” in preventing sand from migrating from the wellbore into the production tubing. Any damage to the installed gravel pack or screen will result in failure of the sand control completion and subsequent production of formation sand. Likewise, plugging of any portion of the sand control completion (caused by fines migration, scale formation, etc.) will result in partial or complete loss of well productivity.
Lack of any redundancy in the event of mechanical damage or production impairment results in the loss of well productivity from single barrier completion designs. Accordingly, there is a need for a well completion apparatus and method to protect the wellbore from gravel pack infiltration in the event of mechanical damage to the well screen. This invention satisfies this need.